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252

TIN AND  ITS ALLOYS

The compositions of various samples of antimony of different origin are as-
follows (Schnabel) :

TABLE  XXXI
Results of Analyses of Antimony

Origin.                   !     Sb
 i
	Cu
	Fe
	Pb
	As
	Bi
	S
	Ni + Co

Hungary (Liptau) .     .    98-27
	o-54
	0-63
	
	__
	0-36
	
	

/-  VJT            (I                          i 98'34
 California -LT                 r   0Z (II   .    .    .   99-081
	O-O2I 0-052
	0-144 0-039
	0-410 0-538
	I -GO 8
 0-036
	
	0-064 0-254
	0-013 trace

Of various origins   )I     98-98
	O-OI
	o-35
	o-34
	0-09
	
	0-23
	__

(analysis by Hilmy) j II \ 98-87
 i
	0-O2
	0-16
	o-73
	0-09
	
	O-II
	

TIN AND  ITS  ALLOYS

Tin is one of the most important metals, being largely used as such and
also as a constituent of numerous industrial alloys.

Methods will be given here for the determination of elements occurring
in commercial tin as impurities, for the analysis of tin-plate and the more
important tin alloys (phosphor-tin, solder, white antifriction metals, type
metal and metal for fittings).

Alloys of tin with copper (bronzes) are considered along with copper.

TIN

Commercial tin is usually contaminated by small quantities of lead,
copper, iron, bismuth, antimony, sulphur, and arsenic and sometimes traces
of molybdenum, tungsten, zinc, manganese, nickel, chromium, etc. The
more important determinations are those of lead, bismuth, copper, iron,
antimony, arsenic and sulphur, qualitative tests for the other elements
being sufficient.

1. Determination of the Lead, Bismuth, Copper and Iron.
According to the greater or less degree of impurity, from 10 to 20 grams
of the sample, flattened on an anvil or in a small rolling mill and cut up
fine, are heated gently on a water-bath with aqua regia (i vol. of nitric
acid with 5 vols. of hydrochloric acid ; 10 grams of the sample require 140
c.c., and 20 grams, 180 c.c.). When the metal is completely attacked, the
liquid is allowed to cool and treated, according to the weight of sample
taken, with 25-35 grams of tartaric acid; the latter is dissolved by gentle
heating, the liquid then rendered alkaline with 20% sodium hydroxide
solution, and 25 c.c. of 2% sodium sulphide solution added with continual
shaking. Separation of the lead, bismuth, copper and ferric sulphides is
facilitated by heating for some time on the water-bath, the precipitate being
ultimately filtered off and washed with dilute sodium sulphide solution.

() DETERMINATION  OF THE LEAD.   The  precipitate  obtained  with the antimony oxide at first separating, excess of